Generally agree 1950 but you've clearly never been to Hamburg. I ended up in the Reeperbahm on a Friday night and witnessed two gangs of transvestites fighting a running street battle, pools of vomit and the salubrious sight of women relieving themselves in the street. Honestly, it made POW Rd look a bit classy. I have to say Prague post 2000 also seems to have deteriorated markedly in terms of public behaviour although this is largely due to British stag and hen parties to be fair.
I think that most cities have dodgy areas but that mostly if you don't look for them you don't find them and I can't imagine that you, like me, spend a lot of time looking for the club scene in any of the places you go to.
Personally part of my filter for picking places to go sadly is where there are generally not many Brits so that when I arrive the locals don't already have an inbuilt contempt for me. Take Valencia over Barcelona - both wonderful cities but the people of Valencia have always been hugely friendly to me whereas I found Barcelona to be a bit more cynical.
I have been to the classic Brit med getaways in my youth but would I go anywhere near them now? Definitely not. It is a real shame that (to be fair mostly younger) Brits abroad seem largely incapable of behaving with any decorum or more importantly respect for the locals. It seems to me that as soon as people leave the country they feel like they can do what they want. Horribly embarrassing for the rest of us who do try to behave well overseas.
it is just depressing that affordable overseas travel which is one of the great privileges we now enjoy and should be a way of learning about other places and cultures and frankly understanding their perspective has turned into lager-fuelled carnage.